This handout photo provided by the Texas Department of Criminal Justice shows Robert Campbell.   Campbell's execution is scheduled for May 13, 2014. (AP Photo/Texas Department of Criminal Justice)
This handout photo provided by the Texas Department of Criminal Justice shows Robert Campbell. Campbell's execution is scheduled for May 13, 2014. (AP Photo/Texas Department of Criminal Justice)
 
MICHAEL GRACZYK, Associated Press

HUNTSVILLE, Texas (AP) — A convicted murderer set for execution in Texas on Tuesday has his hopes pinned on two appeals, including one challenging the state's plan to use a drug for which it will not reveal a source — as was the case with drugs used in a botched execution in Oklahoma two weeks ago.

Robert James Campbell, 41, who was convicted of killing a 20-year-old Houston bank teller, would be the first U.S. inmate put to death since Clayton Lockett's vein collapsed during his lethal injection, prompting Oklahoma prison officials to halt the procedure. Lockett later died of a heart attack.

An investigation is ongoing, but Oklahoma authorities have suggested they believe the trouble there started with Lockett's vein rather than the drugs.

As in Oklahoma, Texas won't say where it gets its execution drugs, saying it needs to protect the producer's identity to prevent threats by death penalty opponents. Unlike Oklahoma, which used a three-drug combination in Lockett's execution, Texas uses a single dose of the sedative pentobarbital to kill inmates.

Lockett writhed and grimaced after the lethal injection was administered, and corrections officials did not realize not all the drug had entered his body for 21 minutes. Campbell's attorneys say Lockett's failed execution proves what many inmates have argued since states turned to made-to-order drugs: that the drugs put the inmates at risk of being subjected to inhumane pain and suffering.

"This is a crucial moment when Texas must recognize that death row prisoners can no longer presume safety unless full disclosure is compelled so that the courts can fully review the lethal injection drugs to be used and ensure that they are safe and legal," said attorney Maurie Levin.

Texas' attorneys say Campbell's claims are speculative and fall "far short" of demonstrating a significant risk of severe pain.

"The Constitution does not require the elimination of all risk of pain," argued Ellen Stewart-Klein, an assistant Texas attorney general.

Campbell's execution would be the eighth this year for Texas, which kills more inmates than any other state, and the fourth in recent weeks to use the compounded pentobarbital. Texas invoked confidentiality in late March when it obtained a new supply of pentobarbital to replace a stock that had reached its expiration date.

Campbell's attorneys went to the U.S. Supreme Court with last-day appeals.

The 5th U.S. Circuit Court of Appeals late Monday rejected an appeal on the drug secrecy issue, saying mere speculation wasn't enough to prove claims Campbell could be subjected to unconstitutionally cruel pain if executed with drugs from Texas' unidentified provider.

Another appeal before the 5th Circuit contends Campbell isn't mentally competent for execution because he has a 69 IQ. Courts generally set a 70 IQ as the minimum threshold. Campbell's attorneys filed a petition to the Supreme Court even before the 5th Circuit ruled on that issue.

Campbell was convicted of capital murder for the 1991 slaying of Alexandra Rendon, who was abducted while putting gas into her car, robbed, raped and shot.

"This was not a shoot and rob and run away," Rendon's cousin, Israel Santana, said. "The agony she had to go through."

Rendon, who had been making wedding plans, was buried wearing her recently purchased wedding dress.